1. Field of the Invention
The present invention relates to a recording format for information data, an information recording/reproducing coding method, an information recording/reproducing encoding circuit, a magnetic recording/reproducing apparatus using these, an information recording/reproducing apparatus and an information communication device respectively for recording/reproducing an information data code at high speed and at high reliability in a high-density mass-storage information recording/reproducing apparatus by magnetic recording and optical recording medium.
2. Description of the Related Art
To realize information recording system at high speed and at high recording density, signal processing technique for faithfully reproducing information recorded on a recording medium plays an important role. Above all, in a mass-storage memory device represented by a high-density magnetic recording/reproducing apparatus, not only to secure the reliability of data recorded for a long term but to prevent various noise disturbance caused by high-density recording and the quality deterioration of recorded/reproduced signal caused by the minuteness of a recorded element due to high-density recording and realize lower-cost and high-density information recording apparatus, higher-precision data conversion technique from a recorded/reproduced signal to information data is desired.
For signal processing technique developed as technique for solving the above-mentioned technical problems and currently applied to magnetic disk products widely, there is a PRML technique in which a partial-response equalization method and a maximum-likelihood decoding method are combined, for example, a method of embodiment is disclosed in detail in a nonpatent reference document 1, “A PRML System for Digital Magnetic Recording” (IEEE Journal of Selected Areas on Communications, vol. 10, pp. 38 to 56, Jan. 1992) and demodulation from a reproduced signal to data at lower signal-to-noise (SN) ratio is enabled by disclosed technique, relieving the problem of intersymbol interference caused by high-density recording.
In the meantime, for a method to keep the data reliability in a general memory device, means for correcting code errors caused in reproduced data by using error-correction coding technique is widely known and a coding method based upon classical algebraic code system, above all, error-correction coding technique such as Reed-Solomon code is most widely applied to a mass-storage recording device. The Reed-Solomon code can correct the predetermined number of code errors caused in a reproduced code sequence in units of code symbol of predetermined bit length by adding a redundant code symbol for checking the code errors into a recorded code sequence beforehand.
Generally, in case the code symbol unit has n-bit length, a code sequence composed of maximum 2(n−1) symbols can be formed and arbitrary t pieces of error symbols in the code sequence can be corrected by adding 2t pieces of redundant code symbols. As described above, as guaranty for error correction for a reproduced code sequence can be easily defined using a Reed-Solomon code that can set maximum correction capability in units of symbol maximum number of correctable error symbol and powerful error-correction processing in which an arbitrary code error event within the maximum number of corrected symbols can be corrected can be realized, the Reed-Solomon code is widely applied to a recording device and for general technique for guaranteeing the reliability of data, the Reed-Solomon code greatly contributes to high-density information recording.
However, to realize further higher-density recording, the increase of code error allowable capability by the enhancement of error-correction coding technique is required. To enhance the error-correction capability, a method of increasing the number of redundant code symbols is easy, however, in the meantime, in information recording, as the increase of redundant code symbols requires the further increase of effective recording density, the method itself is in a limited use.
For another method of enhancing the capability of error-correction coding without increasing redundant code symbols, there is an error-correction decoding method using soft-output information and for new coding technique in which maximum-likelihood decoding by soft-output iterative decoding is executed corresponding to error-correction coding, recently the application of error-correction technique by Turbo coding has been introduced mainly to a data communication field. The Turbo coding technique was proposed by C. Berrou and others in 1993 and is disclosed in a nonpatent reference document 2, “Near Shannon Limit Error-Correcting Coding and Decoding: Turbo-codes” (IEEE Proceedings of International Conference on Communications, pp. 1064 to 1070, May 1993) for example.
The Turbo coding technique executes a concatenated coding that plural code sequences acquired by permuting (interleaving) the same information code sequence at random are generated, simple error-correction coding to generate is applied to each of the plural code sequences and the plural redundant codes are added to the information code sequence. Besides, in decoding, the technique executes an iterative technique that soft-output decoding is individually executed using each of the plural redundant codes for error-correction coding, when one soft-output decoding is executed, the result of maximum-likelihood code sequences for the whole code sequence can be gradually acquired by executing iterative decoding utilizing the results of the other soft-output decoding as the prior information of each code. As described above, the Turbo coding technique is provided with means for realizing optimum decoding for random coding and is technique highlighted as a method of coding and decoding for transmission for realizing a coding gain close to Shannon limit bound on realistic circuit scale. Similarly, a random code error caused in a reproduced code sequence can be powerfully corrected by applying the technique to a recording/reproduction system of an information recording apparatus and it can be expected that a gain limit of near optimum by the addition of code redundancy is achieved on realistic hardware scale and at realistic speed.
However, in an actual magnetic recording/reproducing apparatus, as a defect which may exist on a magnetic recording medium and a continuous bursty signal defect caused by the accidental touch of a magnetic head/medium system exist in addition to a random code error caused by noise, means for efficiently improving both factors of code errors by both is required. In such signal environment, in the above-mentioned Turbo coding technique, the above-mentioned principle effectively acts on the former random code error and extremely high code correcting capability can be fulfilled, however, in the meantime, for the latter burst defect, as the soft-output information of an individual code cannot be suitably generated, the proper correcting capability cannot be fulfilled. Or a code error cannot be also extremely rarely corrected for the superimposition of specific random noise and in these cases, a code error is finally diffused (propagated) and increased in the whole code sequence due to the random permutation (interleave) of an information code sequence.
Besides, in a patent document 1 (Japanese published unexamined patent application No. 2001-285080), a decoder that detects loss in decoding using a convolutional interleaver is disclosed, however, means for solving the above-mentioned problems is not provided.
In such a situation of the prior art, even if error-correction means based upon the Reed-Solomon code is added, the recovery of data cannot be guaranteed and it is extremely difficult to apply the Turbo coding principle in configuration heretofore disclosed to a mass-storage recording/reproduction device for which reliable data integrity is required. Besides, in coding/decoding means by hard-decision algebraic means such as the Reed-Solomon code, the correctable number of correctable code errors is disclosed beforehand and code design is enabled, however, in Turbo coding, as error detection/correction are executed based upon soft-output information, the correctable number of code errors cannot be disclosed. This makes the reliable design of a data recording/reproduction device for enhancing high recording density and high-speed data transfer rate in the prior art extremely difficult and makes the application of Turbo coding to the device more difficult.
[Nonpatent Document 1]
“A PRML System for Digital Magnetic Recording” (IEEE Journal of Selected Areas on Communications, vol. 10, pp. 38 to 56, Jan. 1992)
[Nonpatent Document 2]
“Near Shannon Limit Error-Correcting Coding and Decoding: Turbo-codes” (IEEE Proceedings of International Conference on Communications, pp. 1064 to 1070, May 1993)
[Patent Document 1]
Japanese published unexamined patent application No. 2001-285080